cylinder head coating-cool thing?

[motoman]

The aircraft guys always have interesting articles about their air cooled engines. Perhaps 'cause they can't just jump off and walk home. For your thought....

A new cylinder head will run hotter than one with combustion coating. The coating helps keep the combustion heat from conducting into the head so quickly so that "extra" heat goes out the exhaust port. I had read about ceramic coatings before. They are expensive.

Many of you know that oil splash from the sump cools the underside of the piston also contributing to a cooler mating surface with the head. Knowledge can set us free?

 

[lewb]

I have heard of coating piston in a high powered 2-stroke to help from burning a hole it in. I would guess if the coating would keep the heat from transferring to cylinder and direct to exhaust I would think it would work. Do they shim cylinder head for possible compression issue or maybe that is not an issue taking up some of the area of the combustion chamber with a coating?


I had some interesting results with reduced oil temp using energy release. Basically my 01 chevy 6.0 will go for several thousand miles over the normal oil change algorithm (light tells you when it time to change usually 5 to 7000 miles on normal driving based on RPM and oil temp). I am not anyway involved with ER. When you bring up oil additives is kind of like trying to convince someone to join a cult which I understand. I would think a air cooled lawnmower engine would be a good candidate to see if ER would make a difference. EnergyRelease::Energy Release®

 

[motoman]

I think the ceramic coatings are real thin so maybe no comp ratio problem. I thought this thread might see response from those who have suggested decarbonizing periodically to avoid hot spots and pre detonation. Perhaps a "good" coating is the byproduct of proper mixture strength (tan hard deposits) while the ac lawnmower engines as a class may see more black carbon from bad/worn ring - bore due to overheat and cold/intermittent use. This I do not know.

Edit :Re hot 2 stroke exhaust...Some two stroke cart guys install temperature probes in the exhaust stream to help adjust tune. (trivia)

 

[gainestruk]

Yes that coating is very expensive, in 1990 it was around $500 per engine, I never tried to paint engine after I overhauled one as we had a paint specialist, when he finished the entire engine was coated and it was very hard coating.
I never ran a new overhaul more than a few minutes before paint just to insure all was well.

I did notice before paint in a 10 min run the cylinders were a lot hotter than block but after paint it would move more heat to block, I never test flew a new engine without the paint so I have never seen how it would effect the oil temp.

I do know there are many older engines flying that were overhauled and only have what was left of original paint.
If I needed a new cylinder barrel say from Lycoming it would come only primed.

There is nothing in rules that if you owned an airplane as long as it wasn't used for hire you can do any engine work and just report it in log book and sign off on it.
My next door neighbor rebuilt his engine one cylinder at a time as he could come up with money, it was never painted and he flew it for many years with no issues.

I would think a small engine would bennifet from the coating but it would increase cost by quite a bit.

 

[motoman]

Mike, Thanks for your comments. Another item of interest is the black painting of ac engine cylinders. That goes back a long way. But there is a caution that only a very thin coating is beneficial. On the tractor castings it may simply be too expensive to properly deburr and otherwise prepare the fins for painting for the marginal improvement.